1. Field of the Invention
The present invention relates to a ball screw device, and more particularly to a ball screw device including a cooling structure for suitably cooling the ball nut and for preventing the ball nut from being overheated when the elongated screw shaft is rotated in a great speed relative to the ball nut.
2. Description of the Prior Art
Typical ball screw devices comprise two movable members, such as an elongated screw shaft and a ball nut, rotatable or movable relative to each other, and a number of ball bearing elements disposed between the two movable members for facilitating the sliding movement between the two movable members and/or for allowing the two movable members to be moved or rotated relative to each other in a great rotational speed.
A great heat may be generated between the two movable members or the ball nut and the elongated screw shaft when the two movable members are moved or rotated relative to each other in a great rotational speed, and a cooling structure is thus required to be provided or formed in the ball nut or the elongated screw shaft for suitably cooling the ball nut or the elongated screw shaft, and for preventing the ball nut or the elongated screw shaft from being overheated when the elongated screw shaft is rotated in a great speed relative to the ball nut.
For example, U.S. Pat. No. 6,817,260 to Liao discloses one of the typical ball screw devices comprising a ball nut pivotally or rotatably coupled onto a screw shaft, and a helically running threaded channel provided between the screw shaft and the ball nut for receiving a number of loaded ball bearing elements and for facilitating the sliding or rotating movement between the screw shaft and the ball nut and for allowing the screw shaft and the ball nut to be moved or rotated relative to each other in a great rotational speed, and a cooling structure is formed in the typical ball screw device and includes a peripheral cavity formed between an outer cover and the ball nut as a pathway for cooling agent so as to deprive the ball nut of generated heat therein.
However, the outer cover may not be solidly attached or secured onto the ball nut, and a water tight seal may not be formed between the outer cover and the ball nut such that the cooling agent received in the peripheral cavity that is formed between the outer cover and the ball nut may have a good chance to be leaked or flown out of the outer cover and the ball nut.
The present invention has arisen to mitigate and/or obviate the afore-described disadvantages of the conventional ball screw devices.